My daughters won't help me.... they might break a nail.

 

The only way to remove the dot 3 or 4 is to replace everything rubber in the system a flush with denatured alcohol. then you can add the dot5. Your best bet is dot4 and change it every 2 years.

 

Here's some stuff I dug up...

Hydraulic Fluid
Hydraulic fluids are liquids that are composed of a variety of chemicals. They are used in automobile automatic transmissions, brakes, and power steering; fork lift trucks; tractors; bulldozers; industrial machinery; and airplanes.

Types of hydraulic fluids
The various materials in use as hydraulic fluids range from water to inorganic salt solutions to water oil emulsions, synthetic and naturally occurring organic materials. Water was the first hydraulic fluid used during the early stages of industrial revolution. Presently, petroleum based hydrocarbon type fluids are in wide use. A good hydraulic fluid comprises of:

Good Lubricity
A hydraulic system has various components that contain surfaces that are in close contact and move in relation to each other. A good hydraulic fluid must protect against wear and separate & lubricate such surfaces.

Stable Viscosity
Viscosity is a vital fluid property that varies with temperature and pressure. Fluids having large changes of viscosity with temperature are commonly referred as low viscosity index fluids and those having small changes of viscosity with temperature are known as high viscosity index fluids.

Chemical and Physical Stability
The characteristics of a fluid should remain unchanged during an extended useful life. Since many aspects of stability are chemical in nature, the temperatures to which the fluid will be exposed is an important criterion in the selection of a hydraulic fluid.

System Compatibility
The hydraulic fluid should be inert to materials used in or near the hydraulic equipment. If the fluid in anyway attacks, destroys, dissolves or changes parts of the hydraulic system, the system may lose its functional efficiency and may start malfunctioning.

Good Heat Dissipation
Pressure drops, mechanical friction, fluid friction, leakages, all generate heat. The fluid must carry the generated heat away and readily dissipate it to the atmosphere or coolers.

Flash Point
The flash point of a hydraulic oil is defined as the temperature at which flashes will be generated when the oil is brought into contact with any heated matter.

Fire Resistant
The hydraulic liquids are petroleum derivatives and thus for critical applications, artificial or synthetic hydraulic fluids are used which have high fire resistances. Various grades of fluids with high water content are also available nowadays for oil hydraulic systems.

Prevent Rust Formation
Moisture and oxygen cause rusting of iron parts in the system that can lead to abrasive wear of system components and also act as catalyst to increase the rate of oxidation of the fluid. Fluids with rust inhibitors minimize rust formation in the system.

Low in Volatility
The fluid should posses low vapor pressure or high boiling point characteristic. The vapor pressure of a fluid varies with temperature and hence the operating temperature range of the system is important in determining the suitability of the fluid.

Low Coefficient of Expansion
The hydraulic fluid should have a low coefficient of expansion to minimize the total volume of the system required at the operating temperature.

 

You're speculating. How can you say that's why they chose to use DOT 3 rather than DOT 5. Your opinion may be valid to some extent, but to speak for auto manufactures in a matter-of-fact way looks

 

Well..... yeh.... that's what I believe... so what do you think is the reason?

Maybe you have a better one? eh?

Let's hear ya.. we all need to learn from each other... this is a "forum"

edit: Here's another opinion... says they don't want to invest $$$ in it...

http://www.mg-sportcars.co.uk/Brake_..._Questions.htm


Silicone Brake Fluids

Silicone, or DOT 5 Brake Fluids are based on polydimethyl siloxane and are specialist fluids intended for racing applications. Silicone Brake Fluids may be used in conventional braking systems, as they are compatible with the standard brake components. However, they do not mix with conventional Brake Fluids and should only be considered for use after a complete brake system drain and overhaul. Mixtures of Silicone and conventional Brake Fluid may result in additives transferring between the phases thus resulting in reduced performance. However, because they do not absorb moisture as readily, they tend to last much longer in service. In addition, to the enthusiast that values his/her paintwork, they are much kinder than the normal brake fluid formulations. To this end, classic car enthusiasts often use this. However, be aware that the Bulk Modulus of silicone fluids is lees than that of normal brake fluids, and because of this slight compressibility, it can lead to a slightly spongy pedal feel. This is because ideally, one would work with differing master and slave cylinder dimensions to overcome this property,

but since so few OEMs are willing to invest in this, silicon has failed to achieve any OEM or motor manufacturer approval.

$$$$$$$$$$$

 

I would have said the same thing as you, but I would have add IMO first

I don't think cost is such a factor tho. BMW or MB would have no trouble at all passing on the extra cost to the new car buyer. I'd be guessing to why car manf's do what they do. When I worked at BMW, one of the few things we couldn't defer from were brake pads & fluid. It had to be BMW, period. Some customers were racers with M-3's & M-5's & they would bring in their own racing type fluid (Not syn). We kept a special pressue bleeder separate from the regular BMW fluid bleeder for just that. The service writers would add that on the invoice to cover the dealership. I think it was some type of Hi-temp reg fluid, cant remember. The good thing about the pressure bleeder is that is easy to flush out the system, but you need to use a lot of fluid.

As far as the reg BMW fluid (DOT 3 or 4, not sure), BMW recommends that the system be flushed out completely every 4 years. Usually, 4-year-old brake fluid looks like mud due to all of the water contamination. Once it's cleaned up, there is no sign of rust or corrosion in the system. I've never seen a leaking brake caliper during my 3 years there (even on the cars that weren't maintained too well). I think they stick to old fashion brake fluid because they know it works & they don't have any issues with it. DOT 5 has too many mysteries, plus it's issues with ABS as you've stated.

 

That sounds pretty good.

Relative to C2/C3 calipers though... they are a different design and they do get rusted & pitted. That is why they get stainless sleeves.

When I bought my C2 around 1975, the calipers were all original, and they were so pitted they couldn't be repaired by honing. At that time, you could buy caliper halves directly from GM. I started buying calipers, 1/2 at a time. About a year later, I noticed a few companies were sleeving the calipers, and DOT 5 appeared on the scene, After seeing the DOT 3 damage first hand, I chose to use DOT 5 and haven't looked back. The brakes on the C2 are "hard as a rock".... I cannot notice any compressibiliy issues.... although I do believe compressibillity is notable under the right circumstances.

Since I worked as a "professional" mechanic, I did brake jobs on many different design brake systems... and they were all DOT 3. The calipers and pistons will pit right along with the wheel cylinders. I just finished up a 1997 Nissan... DOT 3... and had to replace the wheel cylinders because they were all oxidized (aluminum) & leaking. There was brake fluid all over the tires & wheel wells.The week before... it was a Toyota.... same story.

I have a set of Kelsey-Hayes front calipers off a 1966 Ford ex-police car sitting in a box in the corner... these have pitted pistons in them... I remember pulling them off & taking them apart and finding the pits in the chrome plated steel pistons.

History repeats.

On the power bleeding question... one of the above links implies that unless your power bleeder has a diaphragm separating the fluid from the pressurized air, you are "pressurizing" water & air right into the brake fluid when you bleed. So a cheap, non-bladder type pressure bleeder is a no-no.... it just compounds the problem. That's not MY statement... but thought it was worth mentioning. Since I now work in a research lab and deal with ultra high vacuum, high pressures, high temps and "outgassing" issues on a daily basis (in a clean room environment), what they say is plausible.

Bottom line... it doesn't matter what people write, or what we read. What matters is what occurs in the "field". Engineers can design all day long and still miss basic laws of physics/nature.

My "opinion/philosophy" is based on work that I have done in the field.... not work that somebody else has done. Based on that work (not books or theory or web sites) I have learned by "doing". Just trying to pass along my experience as a professional mechanic so others can benefit. Best thing though, is to just try it yourself and see what happens. But you have to do the job right, or your conclusions will be tainted.... and you'll just be passing along "bad science".

I try real hard not to be guilty of that.

 

Have dot 5 done by tom454 and you can't go wrong.
1st time-ers Do it yourself and entertain us with your success/failures.
it is a win/win situation

 

Well...as always....you guys have educated me about brake fluids far beyond what I expected. I've followed this from top to bottom and can now make my own decision. Damn the cost....DOT-5 for me.
As stated in the opening post, my system is squeeky clean. After reading the overwhelming replies...I even went to lengths flushing the system with alchohol this past weekend. (Flushed 'MY" bodily system with alchohol too)
Thanks to one and all for this education.

Tom454: A tip of the mug to you
Eddie

 

Hi Eddie
I've checked & it looks like I've been running silicon DOT5 in my bike since 1986. It's been changed twice (both times due to the braided hose being replaced due to fraying of the braiding) & both times it was as clean as a whistle.

Pooling of water: As you know, a bike's master cylinder is exposed to the elements & the breather hole is an ideal place for water to get in, unlike a car. How many brake callipers (cast iron ala Vette) have I had to change/rebuild over the last 20 years for people due to internal corrosion? Bl**dy loads, it's a PITA. Never had to touch mine, or the wife's, or any of several other bikes I built for people & filled with silicon DOT5. The trick is to put DOT5 into a clean system, not one with old "normal" fluid in it, as that's when problems can occur (although I've known people push old fluid out of a system with the new silicon fluid and never have any problems afterwards). If a system is running DOT5 silicon fluid & it gets water pooling in it then the question shouldn't be "what you running DOT5 for?", it should be "How in the hell is water getting into the braking system????" (bearing in mind that DOT5 silicon doesn't have the knack of sucking in water from it's surroundings).

cost: Yeah, does it! Whatever you do, don't get any in a bottle with "Harley Davidson" written on it! Man, that stuff's expensive!

performance: Not noticed any problems at all. Running it in a system that relies on brute strength to stop me (no brake booster) I think that I'd notice any spongy pedal/lever. I don't. I've also spent a day riding as fast as possible (coz it was fun ) up & down a mountain road near the Mediteranean. I've also ridden at altitude through the Pyrenees, two up with camping gear & luggage & both times I turned my brake rotors blue with heat. Not once did I notice any problems with the brakes (I probably wouldn't be writing this if there were, a lot of those bends had a cliff face one side & a sheer drop the other). I did get some fade on the rear brake, but am convinced that it was due to the normal road pads not being able to take the heat (people running normal fluid also report brake fade with the same pads under high heat conditions).

Downsides: One that comes to mind is that bubbles sit in silicon fluid for ages, making bleeding of the system a chore. DO NOT pump the lever as you would normally, use slow depressions & only go about 1/2 its travel (on the basis that the master cylinder is never used for it's full travel normally). Also wait between presses of the pedal. Having a transparent master cylinder reservoir makes it easier to see what's happening. When a bubble rises from the master cylinder it rises very slowly. Pressing the brake again will draw fluid into the MS, often pulling in the bubble that you expelled on the last go.
As bubbles take an age to rise through the lines (especially if the fluid has turned frothy) then rotor runout that causes air to be sucked in at the calipers will be a major headache. Either sort out the runout or fit 'O' ring calipers (preferably both).
If you've had some enthusiastic pumping (of the brake pedal), & the fluid has turned frothy, then go away, have a beer or something & let the small bubbles rise/combine, otherwise you'll be at it all day.
Other downsides are the constant criticisms from people about it. So many people fill an old dirty system with silicon fluid & get problems from it & then tell me that my brakes won't work with silicon fluid that it's unreal. It's no different to people who decide to run their old engines on vegetable oil (Castrol "R" - worth running just for the smell ) & then gum them up as they left some dino oil in there. So who's fault would that be then? The oil, or the person that changed it?
One other thing is that it doesn't eat paint. This is a good thing normally, but a leak in the brake system under a car can often be spotted by paint peeling/bubbling, but these visible signs wouldn't be there with silicon fluid leaking out.

The real world? How many cars are running brake fluid that is filthy & hasn't been changed in years? Will those brake systems be performing better than a well cared for sytem with silicon fluid in it? I remember helping a mate renew the fluid in a 911 turbo. The fluid had been in there for years, was full of crud & was filthy as it came out, so we had to run lots of fresh fluid through to clean it out. The owner later complained about the amount of labour & materials my mate had charged him because "the brakes don't feel any different. Are you trying to pull a fast one on me?".
I don't care what the internet says, I've used the stuff for years & haven't got a single complaint about it (not even the price - it's saved me $$$s as I haven't had to regularly change the fluid due to water ingress). You must remember that with anything to do with brakes the manufacturers are going to cover their asses in these days of litigation so are unlikely to recommend anything other than what they developed the brakes with. If there were potential problems then our governments would have banned it long ago. Each year more & more safety checks, rules & regs come in for car annual inspections, there's a whole army of pen-pushers creating the perfect nanny state & if there was a suspected safety issue with silicon brake fluid then they'd soon be on the case. A long time mechanic I know is of the opinion that manufacturers wouldn't specify it anyway as it would stop people booking their cars in for service work (changing the brake fluid every year or 2 along with all the little "while we were at it" jobs charged at $100/hour + parts, materials & sundry items, plus valet service for the mess they made doing it).
I've got AP Lockheed brakes on my bike & here's some advice I found on them:
-----------------
DOT 5 does not damage paint like other brake fluids do, but is not recommended by AP Lockheed for use in their systems due to higher wear than with other type fluids.

Brake system contamination:

The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil, etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some owners change to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. Brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

British Cycle Supply Company does not recommend use of DOT 5 silicone brake fluid on British motorcycles equipped with any AP Lockeed disc brake components.
----------------
First thing that stands out here is increased wear. Hmmm, in over 20 years of using it (& over 100 000 miles, some of them (a lot!) done with repeated heavy braking from high speed) I've not noticed any wear at all. As they say it causes higher wear then I'll believe them. But, from personal experience over 25 years of using their brakes, silicon fluid causes nowhere near the wear that normal fluid does when not changed regularly. "Is not recommended" doesn't mean "Do not use". My bike & my Vette are both the same age & both have cast brake calipers. The calipers on the bike are fine after running silicon fluid since '86, the calipers on the Vette got changed out for 'O' ring VBP ones last year due to internal corrosion, a suddenly spongy brake pedal that needed pumping to get full brake efficiency & fluid pissing down the inside wall of the tire.
Second thing is the mention of not using alcohol to flush the system
Third is not recommending it for use. I checked up on this and the reason for it appears that they don't trust people to get all the old crud & fluid out of the system, leading to the potential faults mentioned.

I'd say take your pick! I've got no problem with silicon DOT5 for street use (on a racetrack I'd use normal fluid, not because I don't trust silicon fluid, but because the brakes would be taking a pounding & I'd want every smidgen of efficiency I could get. And I wouldn't dream of using stock C3 brakes on a racetrack anyway - I think they'd be the limitation, not the fluid in them). But I run DOT4 in the Vette. The reason for this is that I can't be bothered to dismantle a fully working system just to change the type of fluid its running. I don't trust the Vette's braking system (esp after reading all the posts on here about problems with them!) so being forced to change the fluid once a year makes me get underneath & give it a good checkout. If I did have a completely cleaned out brake system then I think I'd still run DOT4 afterwards. The advantages of silicon would be lost on it as if I spilt any then it's just some flat black paint on the firewall that'll take a hit (not an expensive paintjob) &, as above, I like to be forced into checking the system out once a year. There is a big disadvantage for me in that DOT5 silicon fluid can be hard to find at times. I needed some once (a stainless steel bleed nipple was bleeding fluid up its threads so the resorvior nearly emptied b4 I noticed it). No gas station sold any, the only place open was a bike shop, hence the HD brake fluid - & a couple of bottles of that stuff would pay for a paintjob!

 

IMO better to have the brake fluid ABSORB the water so that the water can be REMOVED when the brake system is periodically flushed.

Water IS going to get into the system, the question is: are you going to remove it (DOT 3) or possibly let it be trapped (DOT 5).

 

Not that this should have any bearing on the choice, but I've read that silicone fluid was developed for the US military primarily for it's ability to withstand temperature extremes with minimal change in viscosity. I assume the excessively harsh environments that their equipment operates within also put a beating on ANYTHING that can be damaged by water infiltration, so, again, silicone was specified to solve their unique problem. They didn't need ultra-low compressibility for mico-modulation, as would be needed in a racecar. They didn't want to be broke down in hostile territory because the fluid froze in -50 F temps or sludged up and bound up the MC...

 

As I said b4, how is much water getting into the system when running DOT5? OK, so there'll be minute quantities condensing out of the air in the fluid reservoir, but the silicon fluid isn't actively attracting it from the air like DOT3 or 4 fluids do. The master cylinder is under the hood, well out of the way of water, & if water is entering the system elsewhere then there's a problem in the system that's more important than water getting into the fluid ie a leak. Or is there some way that a booster can cause water to enter the system?
Removing the water while changing DOT3 is fine in theory, but what damage has it done while it's been in there? Last summer I had to waste a day repairing a leaking slave cylinder on my wife's MGB. It was leaking because the aluminium surface had corroded due to water being in contact with it, yet the fluid was religiously changed each year. And now the stupid thing has started leaking again, probably for the same reason. This appears, from talking to members of the owners club, to be a common problem, except in the ones running silicon brake fluid.

What I'll do, out of curiosity, is pull the front brake of my bike apart (which'll be a lot easier than pulling the Vette's system apart!). It's got a st/st master cylinder, but at the lowest point in the system is a cast iron caliper. I'll carefully remove it & pour the contents of the caliper out & check for water & also for corrosion in it. The caliper I checked from the Vette, & the MGB slave cylinder, looked badly corroded inside (amazing that they were sealing at all) so it'd be interesting seeing what nearly 20 years of silicon DOT5 use has done to the inside of a caliper. I'll treat it as a safety measure: I've only got 2 brakes on the bike - at least with the Vette I've also got a highly efficient emergency brake to pull me up if the brakes fail

 

as far as going to 3 from 5,
i found the comment about it never clearing out to be untrue.
the green gook is gone in just 10 years

 

HI PAUL Thanks for all your info. A great read. Ya know...you should have been a writer!!!
Eddie